--- a/dwtx/jface/action/ContributionManager.d	Mon May 19 13:41:06 2008 +0200
+++ b/dwtx/jface/action/ContributionManager.d	Thu May 22 01:36:46 2008 +0200
@@ -22,6 +22,7 @@
 import tango.util.collection.ArraySeq;
 import tango.util.collection.model.Seq;
 
+import dwtx.core.runtime.Assert;
 import dwtx.jface.util.Policy;
 
 import dwt.dwthelper.utils;
@@ -85,6 +86,7 @@
      * (non-Javadoc) Method declared on IContributionManager.
      */
     public void add(IAction action) {
+        Assert.isNotNull(action, "Action must not be null"); //$NON-NLS-1$
         add(new ActionContributionItem(action));
     }
 
@@ -92,6 +94,7 @@
      * (non-Javadoc) Method declared on IContributionManager.
      */
     public void add(IContributionItem item) {
+        Assert.isNotNull(item, "Item must not be null"); //$NON-NLS-1$
         if (allowItem(item)) {
             contributions.append(item);
             itemAdded(item);
@@ -240,7 +243,7 @@
     public IContributionManagerOverrides getOverrides() {
         if (overrides is null) {
             overrides = new class IContributionManagerOverrides {
-                public ValueWrapperBool getEnabled(IContributionItem item) {
+                public Boolean getEnabled(IContributionItem item) {
                     return null;
                 }